1. Field of the Invention
The present invention relates to a power-supply apparatus and its mounting-completion indication method. The power-supply apparatus is used by incorporating a dry cell, or dry cells, in its body and mounting the body to a device.
2. Description of the Related Art
The following description of a battery pack, having a remaining-capacity indication, has been used as a power-supply apparatus for portable camcorders and portable computers. FIG. 9 shows a circuit diagram of the electric configuration of a conventional battery pack. The battery pack has a one-chip CPU 101, including an analog-to-digital converter 102; a resistor 103, for measuring a dry-cell charging current and discharging current; dry cells 104; a thermistor 105, for measuring the surface temperature of the dry cells 104; and LEDs 106, for indicating the remaining capacity of the dry cells 104. According to the remaining capacity of the dry cells, the number of LEDs lit changes. When the remaining capacity is 20% of the full capacitance, for example, one of the LEDs 106 lights. When the remaining capacity equals the full capacitance, all five of the LEDs 106 light. The battery pack further includes a push-button switch 107 for triggering the remaining-capacity indication, the switch causing the LEDs 106 to light for about three seconds when pressed once, then to go off; a positive terminal 108 of the battery pack connected to a device; and a negative terminal 109 of the battery pack connected to the device. The remaining capacity is calculated in the following way. The CPU 101 stores the initial capacity of the dry cells 104 in advance. The CPU obtains a charging current or discharging current from the voltage across the resistor 103, and calculates the remaining capacity. Assuming that the voltages at each end of the resistor 103, having a resistance of R, are a and b, respectively, the voltage difference between a and b is measured using the analog-to-digital converter 102 (voltage b is the voltage output from the dry cells 104). When a is smaller than b, the dry cells are determined to be being discharged. When a is larger than b, the dry cells are determined to be charging. The flowing current is calculated from equation (1) described below, using the voltage across the resistor 103. EQU Charging or discharging current=(.vertline.a-b.vertline./resistance R).times.efficiency (1)
The charging efficiency and discharging efficiency are determined in advance according to the temperature. The temperature of the dry cells 104 is detected by the thermistor 105 as a voltage. The voltage is converted to a digital value, which the CPU 101 can deal with, by the analog-to-digital converter.
A current value, per unit of time calculated using expression (1), is added to the initial capacity when charging, and is subtracted from the initial capacity when discharging.
However, when a conventional battery pack is mounted to a device, there is no way to determine whether the battery pack has been correctly mounted to the device. In addition, it is difficult for a user to check the remaining capacity of the dry cells before using them, because the user must press the push-button switch 107 to check the remaining capacity. If the LEDs 106 are turned on to indicate the remaining capacity, the dry cells are then consumed, even when they are not being used for their intended purposes. When none of the LEDs 106 light, it cannot be determined whether the dry cells have completely discharged, or whether the battery is defective or mounted incorrectly. That is inconvenient.